This invention relates to a machine for sorting cereal grain, plastic pellets, coffee beans and other granular materials, and more particularly to an improvement of a photoelectric detection device or optical detector in a color-sorting machine for granular materials.
The color-sorting machine for granular materials discussed here is of the type comprising a raw material supply device, a transport device that drops the raw material grains fed from the supply unit in a substantially fixed locus or path, an optical detection device provided along the raw material grain drop path for optically detecting the falling raw material grains, and a sorting device for removing no-good grains. The machine detects changes in the quantity of received light from no-good grains, namely colored grains and foreign matters such as glass, pebbles, etc., passing along the coming-down path, through the optical detection device, and operates the sorting device based on the value of the detection signal to sort the no-good grains out of the raw material grains by, for instance, blowing them away by means of air jet or the like.
There are optical detection devices known as this type, which illuminate the raw material grains with light, separate the reflected light into the respective wavelengths of red and green or red, green and blue, optically detect each wavelength by means of visible light sensors and discriminate grains with specific colors that make them no-good, based on the detection values obtained.
An example of such an optical detection device will be described with reference to FIG. 5. The optical detection device shown in the figure is provided with an optical detection unit 300 which comprises a condenser lens 350, a color separation prism 360, and two visible light sensors 330 and 330. The color separation prism 360 is adapted to separate the light reflected from the raw material grains G to be sorted into a red wavelength and a green wavelength and to lead one of the wavelengths, red for example, in a direction perpendicular to the other. The respective wavelengths separated by the prism 360 are incident to the visible light sensor 330 for detecting a red wavelength and the visible light sensor 330 for detecting a green wavelength, which are provided in their paths of progress, respectively, and are detected. Ratio computations, that is color analysis, is carried out on the values of the detected red wavelength and green wavelength, and when these values of the ratio computations are outside of prescribed threshold values, a jet nozzle unit operates and the bad particle of red color is sorted out. Such optical detection devices can be seen in, for example, Japanese Patent Application Laid-Open Publication Nos. 3-62532 and 3-78634.
Further, a granular sorting machine, which sorts out no-good grains, such as colored grains and inorganic impurities of pebbles and glass, from the material to be sorted by means of near infrared light and visible light, is seen in Japanese Patent Application Laid-Open Publication No. 8-229517. As shown in FIG. 6, this color-sorting machine for granular materials is such that the detected light is separated into two wavelengths of near infrared light and visible light by a dichroic mirror 310, and one of these wavelengths is led in a direction perpendicular to the other. The respective wavelengths thus divided are detected by the near infrared light sensor 340 and the visible light ray sensor 330 which are provided in the positions which they pass through. A jet nozzle unit operates according to comparison between the values detected by these sensors and standard values set in advance to sort out no-good grains.
Japanese Patent Application Laid-Open Publication No. 8-229517 also shows an optical detection unit 300 as shown in FIG. 7. This unit includes a sensor section 380 that has a visible light sensor 330 and a near infrared light sensor 340 formed integrally with the former. The optical detection unit 300 detects an optical detection position F1 on the upper side in the coming-down path of the material to be sorted by means of the visible light sensor 330, and an optical detection position F2 on the lower side in the coming-down path is detected by the near infrared light sensor 340.
The color-sorting machines for granular materials as shown in FIGS. 5 and 6, that carry out the detection of a wavelength in the near infrared range and a wavelength in visible range, or the detection of a red wavelength and a green wavelength or red, green and blue wavelengths by means of the single optical detector, split the light from the material being sorted into two or three wavelengths through the dichroic mirror or color separation prism described above, and lead them incident on the light sensors provided in the directions of travel of the respective wavelengths. With this kind of optical detection structure, two or three light-receiving sensors are arranged at right angles to each other around the dichroic mirror or color separation prism, so that the whole optical detection unit becomes large in size. Furthermore, it is necessary to make the light, which is detected from the same grain of the material to be sorted in the same position, incident on the respective sensors. As described above, however, the respective light-receiving sensors are arranged in the positions at right angles to each other, so that positioning of the respective sensors for making the detected light accurately incident to corresponding one of the two or three sensors is very difficult.
On the other hand, the light detection unit 300 shown in FIG. 7 that includes the sensor section 380 having the visible light sensor 330 and the near infrared light sensor 340 formed integrally can provide a solution to the problems of increased size and positioning described above. However, when the light-receiving sensors of the sensor section 380 are comprised of, for example, a visible light sensor for detecting a red wavelength and a visible light sensor for detecting a green wavelength and are used in so-called color sorting based on the respective wavelengths, color sorting cannot be done. The reason is that the red wavelength and the green wavelength are detected at the different light detection positions F1 and F2, respectively, and it is impossible to identify the light detected from F1 and F2 as a red wavelength and a green wavelength from the same grain.